Climatic control on clay mineral formation: Evidence from weathering profiles developed on either side of the Western Ghats

Abstract

Many physico-chemical variables like rock-type, climate, topography and exposure age affect weathering environments. In the present study, an attempt is made to understand how the nature of clay minerals formed due to weathering differs in tropical regions receiving high and low rainfall. Clay mineralogy of weathering profiles in west coast of India, which receives about 3 m rainfall through two monsoons and those from the inland rain-shadow zones (< 200 cm rainfall) are studied using X-ray diffraction technique. In the west coast, 1:1 clays (kaolinite) and Fe-Al oxides (gibbsite/goethite) are dominant clay minerals in the weathering profiles while 2:1 clay minerals are absent or found only in trace amounts. Weathering profiles in the rain shadow region have more complex clay mineralogy and are dominated by 2:1 clays and kaolinite. Fe-Al oxides are either less or absent in clay fraction. The kaolinite-smectite interstratified mineral in Banasandra profiles are formed due to transformation of smectites to kaolinite, which is indicative of a humid paleoclimate. In tropical regions receiving high rainfall the clay mineral assemblage remains the same irrespective of the parent rock type. Rainfall and availability of water apart from temperature, are the most important factors that determine kinetics of chemical weathering. Mineral alteration reactions proceed through different pathways in water rich and water poor environments.

Chemical weathering of monsoonal eastern China: implications from major elements of topsoil

“…Persistent investigations on the controls of chemical weathering have contributed a lot to our understanding on the links between chemical weathering and its controlling factors, such as tectonics (geological settings and topographical conditions) (Raymo et al, 1988;Drever and Zobrist, 1992;Raymo and Ruddiman, 1992;Berner and Berner, 1997;Riebe et al, 2001;Jacobson et al, 2003;West et al, 2005;Liu et al, 2007a,b;Moore et al, 2013); provenance (or lithology of source rock) (Sawyer, 1986;Nesbitt and Wilson, 1992;Le Pera et al, 2001;Dessert et al, 2003;Price and Velbel, 2003;Caspari et al, 2006); climate (temperature, precipitation and runoff) (Velbel, 1993;Brady and Carroll, 1994;White and Blum, 1995;Riebe et al, 2001Riebe et al, , 2004Yang et al, 2004;Deepthy and Balakrishnan, 2005;Singh et al, 2005;West et al, 2005;Liu et al, 2007a,b;Gislason et al, 2008;Gabet et al, 2010;Li and Yang, 2010); vegetation (Berner, 1992;Drever, 1994;Gislason et al, 1996); time (Grantham and Velbel, 1988;Taylor and Blum, 1995;Gislason et al, 1996;White and Brantley, 2003); and even human activities (Motuzova and Hong Van, 1999;Chetelat et al, 2008). Although much work has been done, controversies still remain on the control...…”

“…To solve this problem, various solutions and chemical indices have been established and applied, most of which are based on major element analyses, such as SiO 2 /Al 2 O 3 ratio (Ruxton, 1968), WIP (weathering index of Parker) (Parker, 1970), CIA (chemical index of alteration) (Nesbitt and Young, 1982), CIW (chemical index of weathering) (Harnois, 1988), and ternary diagrams of chemical elements (Nesbitt and Young, 1989;Ohta and Arai, 2007). Good results have been obtained in their applications to the geochemistry of weathering profiles (Nesbitt and Young, 1989;Nesbitt and Wilson, 1992;Ng et al, 2001;Duzgoren-Aydin and Aydin, 2003;Price and Velbel, 2003;Deepthy and Balakrishnan, 2005;Singh et al, 2005;Caspari et al, 2006;Ohta and Arai, 2007;Shao et al, 2012) and river chemistry of dissolved loads (Liu et al, 2004(Liu et al, , 2007a(Liu et al, ,b, 2009Li and Yang, 2010;Shao et al, 2012). In fact, till present, most of our chemical weathering information is obtained from the geochemistry of weathering profiles and river chemistry of dissolved loads.…”

The Origin of Etch Pits Recorded on Residual Grain Surfaces from Kaolinized Granitic Rocks West Region Cameroon

“…-A weathered C horizon (an upper saprolitic zone and a lower saprock zone) (Nahon, 1991;Deepthy and Balakrishnan, 2005), with very thick (300-1500 cm), pale brown to very pale brown (10 YR 8/3), whitish, and yellowish colors with many slighty weathered fragments of granite, and moderately plastic mixed clayey and sandy materials. The weathered granite shows well-preserved structures and shapes of the primary minerals relative to the original rock, with few changes throughout the profile.…”

“…A tremendous amount of literature exits on the mechanism of chemical weathering under different geomorphic and paleoclimatic conditions, provided by many investigators (Stanley, 1968;Lelong, 1969;Pedro, 1964Pedro, , 1968Millot, 1971;Krinsley & Cavallero, 1970;Berner & Holdren, 1979;Nahon et al, 1979Nahon et al, , 1982Tardy, 1993;Kitagawa et al, 1994;Wilson, 1995;Wouatong et al, 1996;Wouatong et al, 2005;Deepthy & Balakrishnan, 2005;Nguetnkam et al, 2008;Ndjigui et al, 2008;Kamgang et al, 2009). The main chemical factors that usually control the weathering of rocks include: solution pH, parent material composition and crystallinity, microenvironment, oxidation-reduction potentials, temperature and ionic strength.…”

Mineralogy and Genesis of Mixed-Layer Illite-Vermiculite in the Homogeneous Red Soil and the Net-Like Red Soil of Xuancheng, China

“…As the ultimate weathering products of the paleosoil, the formation and development of clay minerals are mainly controlled by climate and geological conditions (Deepthy and Balakrishnan, 2005;Merriman, 2002;Singer, 1984). Therefore, the paleoclimate information is well preserved in the clay mineral compositions (Singer, 1980;1984).…”